"""
All customers receive 100 concurrent lines of real-time market data (which can be displayed in TWS or via the API). After the first month of trading, high-volume traders may receive additional lines of market data, calculated as follows:

Maximum ((Monthly Commissions/8), 100)

For example, if you generate USD 16.00 in monthly commissions, you will receive 100 lines of market data. If you generate USD 400.00 in commissions, you will receive 100 lines of market data. But if you generate USD 840.00 in commissions, you will receive 105 lines of market data.
"""

My recollection also is that API data take priority over TWS data in getting to the 100 limit.